High infrared reflection coatings, thin film coating deposition methods, and associated technologies

ABSTRACT

The invention provides low-emissivity coatings that are highly reflective of infrared radiation. The coating includes three infrared-reflection film regions, which may each comprise silver.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Application No.60/725,891, filed Oct. 11, 2005, U.S. patent application Ser. No.11/360,266, filed Feb. 23, 2006, and U.S. patent application Ser. No.11/398,345, filed Apr. 5, 2006, the entire disclosures of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to thin film coatings for glass and othersubstrates. In particular, this invention relates to low-emissivitycoatings that are particularly reflective of infrared radiation. Alsoprovided are methods and equipment for depositing thin film coatings.

BACKGROUND OF THE INVENTION

Low-emissivity coatings are well known in the art. Typically, theyinclude one or two layers of infrared-reflection film and two or morelayers of transparent dielectric film. The infrared-reflection film,which generally is a conductive metal like silver, gold, or copper,reduces the transmission of heat through the coating. The dielectricfilm is used to antireflect the infrared-reflection film and to controlother properties and characteristics of the coating, such as color anddurability. Commonly used dielectric materials include oxides of zinc,tin, indium, bismuth, and titanium, among others.

Most commercially available low-emissivity coatings have one or twosilver layers each sandwiched between two coats of transparentdielectric film. Increasing the number of silver films in alow-emissivity coating can increase its infrared reflection. However,this can also reduce the visible transmission of the coating, and/ornegatively impact the color of the coating, and/or decrease thedurability of the coating. Perhaps for these reasons, low-emissivitycoatings with three silver layers historically have not found much placein the market.

It would be desirable to provide a low-emissivity coating that includesthree infrared-reflection layers and has desirable coating propertiesand characteristics.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph showing the spectral properties of a commerciallyavailable double silver low-emissivity coating.

FIG. 2 is a graph showing the spectral properties of a high infraredreflection coating in accordance with certain embodiments of the presentinvention.

FIG. 3 is a graph comparing the spectral properties of a high infraredreflection coating in accordance with certain embodiments of theinvention against a commercially available double silver low-emissivitycoating.

FIG. 4 is a schematic cross-sectional side view of a substrate bearing ahigh infrared reflection coating in accordance with certain embodimentsof the invention.

FIG. 5 is a schematic partially broken-away cross-sectional side view ofa multiple-pane insulating glazing unit bearing a high infraredreflection coating in accordance with certain embodiments of theinvention.

FIG. 6 is a schematic cross-sectional side view of a coater used incertain embodiments of the invention.

SUMMARY OF THE INVENTION

In certain embodiments, the invention provides a coated transparent pane(e.g., a window pane) having opposed first and second major surfaces. Inthese embodiments, the coated pane is part of a multiple-pane insulatingglazing unit that includes a second pane. The insulating glazing unithas a between-pane space to which the second major surface of thiscoated pane is exposed. In the present group of embodiments, the secondmajor surface bears a low-emissivity coating that has both a sheetresistance of less than 2.5 Ω/square and an emissivity of less than0.03. The low-emissivity coating comprises three infrared-reflectionfilm regions, which in the present embodiments preferably have acombined thickness of at least 425 angstroms. Preferably, the coatedpane in the present embodiments has a visible transmittance of greaterthan 0.60. In some cases, the coated pane has a major dimension of atleast one meter.

Certain embodiments of the invention provide a coated transparent (e.g.,a window pane) having opposed first and second major surfaces. In theseembodiments, the pane is part of a multiple-pane insulating glazing unitthat includes a second pane. The insulating glazing unit has abetween-pane space to which the second major surface of this coated paneis exposed. In the present group of embodiments, the second majorsurface bears a low-emissivity coating that has both a sheet resistanceof less than 3.0 Ω/square and an emissivity of less than 0.03. Thelow-emissivity coating comprises three infrared-reflection film regionsand includes transparent dielectric film between the second majorsurface and that one of the three infrared-reflection film regions thatis nearest the second major surface. In the present embodiments, betweenthe innermost infrared reflection film region and the second majorsurface the coating has less than 190 angstroms of transparentdielectric film having a refractive index of 1.7 or greater. In somecases, the coated pane has a major dimension of at least one meter.

In certain embodiments, the invention provides a coated substrate havinga major surface bearing a low-emissivity coating. Here, the coatingcomprises, from the noted major surface outwardly: a first transparentdielectric film region; a first infrared-reflection film regioncomprising silver; a second transparent dielectric film region; a secondinfrared-reflection film region comprising silver; a third transparentdielectric film region; a third infrared-reflection film regioncomprising silver; and a fourth transparent dielectric film region. Inthe present group of embodiments, the coated substrate has a totalvisible transmission of greater than 55%, the coated substrate has aspectral transmission curve with a transmission peak located within avisible wavelength range, and this spectral transmission curve has ahalfwidth of less than 360 nm.

Certain embodiments provide a substrate having a major surface thatbears a low-emissivity coating. Here, the coating comprises a firstinfrared-reflection film region having a thickness, a secondinfrared-reflection film region having a thickness, and a thirdinfrared-reflection film region having a thickness. In the presentembodiments, the thickness of the third infrared-reflection film regionis greater than the thickness of the second infrared-reflection filmregion, and the thickness of the second infrared-reflection film regionis greater than the thickness of the first infrared-reflection filmregion. The coating includes, from the noted major surface outwardly: afirst transparent dielectric film region; the first infrared-reflectionfilm region; a second transparent dielectric film region; the secondinfrared-reflection film region; a third transparent dielectric filmregion; the third infrared-reflection film region; and a fourthtransparent dielectric film region. Preferably, the first, second, andthird infrared-reflection film regions each comprise silver. In thepresent embodiments, the coating has a first reflection-region ratioequal to the thickness of the first infrared-reflection film region overthe thickness of the second infrared-reflection film region, the coatinghas a second reflection-region ratio equal to the thickness of thesecond infrared-reflection film region over the thickness of the thirdinfrared-reflection film region, and at least one of the first andsecond reflection-region ratios is less than 0.85.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following detailed description is to be read with reference to thedrawings, in which like elements in different drawings have likereference numerals. The drawings, which are not necessarily to scale,depict selected embodiments and are not intended to limit the scope ofthe invention. Skilled artisans will recognize that the examplesprovided herein have many useful alternatives that fall within the scopeof the invention.

Single and double silver low-emissivity coatings have been known in theart for years. Single silver low-emissivity coatings provideadvantageous infrared reflection, commonly in the neighborhood of 97%.Double silver low-emissivity coatings offer further improvements interms of high visible transmission and high infrared reflection. Thereare, however, practical ceilings on the infrared reflection levels thatcan be achieved using a double silver low-emissivity coating. Forexample, while increasing the amount of silver in a double silvercoating may boost the infrared reflection above 97%, the road towardeven higher infrared reflection, e.g., above 98.5%, is difficult toachieve in a double silver coating that requires a balance of otherproperties (high visible transmission, good color, durability, etc.).

FIG. 1 is a graph showing the spectral properties of a highlyadvantageous commercially available double silver low-emissivitycoating. This graph shows transmission (the curve that is upwardlyconvex in the visible wavelength range) and glass-side reflection (thecurve that is downwardly concave in the visible wavelength range) for aglass sheet bearing the double silver low-emissivity coating. While thisparticular double silver coating offers excellent spectral properties,it has been reported that conventional double silver coatings allowanywhere from 5% to 50% transmission in the infrared wavelength range(U.S. Pat. No. 6,262,830, column 6, lines 43-51).

FIG. 2 is a graph showing the spectral properties of a high infraredreflection coating in accordance with certain embodiments of the presentinvention. Here again, the graph shows transmission (the curve that isupwardly convex in the visible wavelength range) and glass-sidereflection (the curve that is downwardly concave in the visiblewavelength range) for a glass sheet bearing the high infrared reflectioncoating.

The infrared reflection for the present coating 7 is much higher thanthat of the double silver coating. This is perhaps best appreciated byreferring to FIG. 3, which is a graph showing both the spectralproperties of the high infrared reflection coating 7 and those of thedouble silver coating. Here, a side-by-side comparison can be made ofthe infrared reflection levels achieved by these two coatings. It can beseen that the present coating 7 achieves a much higher infraredreflection than the double silver coating. It can also be seen that thelevels of visible transmission for these two coatings are comparable.Moreover, the cutoff between visible wavelengths and infraredwavelengths is much sharper for the present coating 7 (the curvesdelineated with solid lines) than for the double silver coating (thecurves delineated with circles). Thus, the high infrared reflectioncoating 7 is believed to provide a quantum leap forward in terms ofenergy efficiency compared to double silver low-emissivity coatings, andeven more so compared to single silver low-emissivity coatings.

The present high infrared reflection coating has a number of beneficialproperties. The ensuing discussion reports several of these properties.In some cases, properties are reported herein for a single (i.e.,monolithic) pane 12 bearing the present coating 7 on one surface 18. Inother cases, these properties are reported for an IG unit 3 having thepresent coating 7 on its #2 surface 18. In such cases, the reportedproperties are for an IG unit wherein both panes are clear 2.2 mm sodalime float glass with a ½ inch between-pane space filled with aninsulative gas mix of 90% argon and 10% air. Of course, these specificsare by no means limiting to the invention. Absent an express statementto the contrary, the present discussion reports determinations madeusing the well known WINDOW 5.2a computer program (e.g., calculatingcenter of glass data) under standard ASHRAE conditions.

As noted above, the high infrared reflection coating 7 providesexceptional thermal insulating properties. The coating 7 comprises threeinfrared-reflection film regions 100, 200, and 300. These film regionsare typically silver or another electrically conductive material, andthey impart exceptionally low sheet resistance in the coating. Forexample, the sheet resistance of the present coating 7 is less than 3.0Ω/square. Preferably, the sheet resistance of this coating 7 is lessthan 2.5 Ω/square (e.g., less than 2.0 Ω/square, less than 1.75Ω/square, or less than 1.5 Ω/square). While the desired level of sheetresistance can be selected and varied to accommodate differentapplications, a number of preferred coating embodiments (e.g., theexemplary film stacks tabulated below) provide a sheet resistance ofless than 1.4 Ω/square, such as about 1.25-1.3 Ω/square. The sheetresistance of the coating can be measured in standard fashion using a4-point probe. Other methods known in the art as being useful forcalculating sheet resistance can also be used.

The coating 7 also has exceptionally low emissivity. For example, theemissivity of the coating 7 is less than 0.06. Preferably, theemissivity of this coating 7 is less than 0.04 (e.g., less than 0.03, oreven less than 0.025). While the desired level of emissivity can beselected and varied to accommodate different applications, a number ofpreferred coating embodiments (e.g., the exemplary film stacks tabulatedbelow) provide an emissivity of less than 0.023, such as about 0.020. Incontrast, an uncoated pane of clear glass would typically have anemissivity of about 0.84.

The term “emissivity” is well known in the present art. This term isused herein in accordance with its well-known meaning to refer to theratio of radiation emitted by a surface to the radiation emitted by ablackbody at the same temperature. Emissivity is a characteristic ofboth absorption and reflectance. It is usually represented by theformula: E=1−Reflectance. The present emissivity values can bedetermined as specified in “Standard Test Method For Emittance OfSpecular Surfaces Using Spectrometric Measurements” NFRC 301-93, theentire teachings of which are incorporated herein by reference.Emissivity can be calculated by multiplying the measured sheetresistance by 0.016866. Using this method, a coating 7 that providessheet resistance of about 1.25, for example, can be determined to havean emissivity of about 0.021.

In addition to low sheet resistance and low emissivity, the presentcoating 7 provides exceptional solar heat gain properties. As is wellknown, the solar heat gain coefficient (SHGC) of a window is thefraction of incident solar radiation that is admitted through a window.There are a number of applications where low solar heat gain windows areof particular benefit. In warm climates, for example, it is especiallydesirable to have low solar heat gain windows. For example, solar heatgain coefficients of about 0.4 and below are generally recommended forbuildings in the southern United States. Further, windows that areexposed to a lot of undesirable sun benefit from having a low solar heatgain coefficient. Windows on the east or west side of a building, forinstance, tend to get a lot of sun in the morning and afternoon. Forapplications like these, the solar heat gain coefficient plays a vitalrole in maintaining a comfortable environment within the building. Thus,it is particularly beneficial to provide windows of this nature withcoatings that establish a low solar heat gain coefficient (i.e., lowsolar heat gain coatings). Low solar heat gain coatings would be highlydesirable for many window applications.

A tradeoff is sometimes made in low solar heat gain coatings whereby thefilms selected to achieve a low SHGC have the effect of decreasing thevisible transmittance to a lower level than is ideal and/or increasingthe visible reflectance to a higher level than is ideal. As aconsequence, windows bearing these coatings may have unacceptably lowvisible transmission and/or a somewhat mirror-like appearance.

The present coating 7 provides an exceptionally low solar heat gaincoefficient. For example, the solar heat gain coefficient of the presentIG unit 3 is less than 0.4. Preferably, the present IG unit 3 has asolar heat gain coefficient of less than 0.35 (e.g., less than 0.33, oreven less than 0.31 in some cases). While the desired SHGC level can beselected and varied to accommodate different applications, somepreferred embodiments (e.g., where the coating 7 is one of the exemplaryfilm stacks tabulated below) provide an IG unit 3 having a solar heatgain coefficient of less than 0.3, such as between 0.25 and 0.29 (e.g.,about 0.27).

The term “solar heat gain coefficient” is used herein in accordance withits well known meaning. Reference is made to NFRC 200-93 (1993), theentire teachings of which are incorporated herein by reference. The SHGCcan be calculated using the methodology embedded in the well knownWINDOW 5.2a computer program.

In combination with the beneficial thermal insulating propertiesdiscussed above, the present coating 7 has exceptional opticalproperties. As noted above, a tradeoff is sometimes made in low solarheat gain coatings whereby the films selected to achieve good thermalinsulating properties have the effect of restricting the visibletransmission to a level that is lower than ideal.

To the contrary, the present coating 7 provides an exceptionalcombination of total visible transmission and thermal insulatingproperties. For example, the present IG unit 3 (and the present pane 12,whether monolithic or as part of the IG unit 3) has a visibletransmittance T_(v) of greater than 0.45 (i.e., greater than 45%).Preferably, the present IG unit 3 (and the present pane 12, whethermonolithic or insulated) achieves a visible transmittance T_(v) ofgreater than 0.55 (e.g., greater than 0.6). While the desired level ofvisible transmittance can be selected and varied to accommodatedifferent applications, certain preferred embodiments (e.g., where thecoating 7 is one of the exemplary film stacks tabulated below) providean IG unit 3 (or a pane 12, which can be monolithic or part of the IGunit 3) having a visible transmittance of greater than 0.65, such asabout 0.66

In one particular group of embodiments, the film region thicknesses andcompositions are selected to achieve a visible transmittance of greaterthan 0.7, greater than 0.71, or even greater than 0.072. In some cases,the film region thicknesses and compositions are selected to achieve avisible transmittance of about 0.73. Here, the infrared-reflection filmregions may be thinned to provide the desired transmittance.

The term “visible transmittance” is well known in the art and is usedherein in accordance with its well-known meaning. Visible transmittance,as well as visible reflectance, can be determined in accordance withNFRC 300, Standard Test Method for Determining the Solar and InfraredOptical Properties of Glazing Materials and Fading Resistance of Systems(National Fenestration Rating Council Incorporated, adopted December2001, published January 2002). The well known WINDOW 5.2a computerprogram can be used in calculating these and other reported opticalproperties.

Preferably, the coated substrate (i.e., the present pane) 12 has aspectral transmission curve with a peak transmission located in thevisible wavelength range. This is readily apparent in FIG. 2. In certainembodiments, this spectral transmission curve has a halfwidth of lessthan 360 nm, less than 320 nm, less than 300 nm, less than 290 nm, lessthan 275 nm, or even less than 250 nm. In these embodiments, the coating7 provides a highly advantageous narrow transmission curve, whichdesirably has high visible transmittance spanning the visible range and,at the same time, provides an exceptionally steep slope between highlytransmitted visible wavelengths and highly reflected infraredwavelengths. In certain embodiments, the coating 7 additionally (i.e.,together with having any maximum halfwidth noted above) or alternativelyachieves a halfwidth that is greater than 50 nm, greater than 100 nm,greater than 150 nm, or even greater than 175 nm. This can be desirablein providing high levels of visible transmittance over a substantialportion of the visible spectrum.

The present coating 7 provides exceptional efficiency in terms of thelow solar heat gain coefficient that is achieved in combination withhigh visible transmission. The ratio of visible transmittance (as afraction of unity) over SHGC is referred to herein as thevisible-thermal efficiency ratio of the present IG unit 3. This ratiopreferably is greater than 2, greater than 2.2, and in some cases evengreater than 2.3. Certain preferred embodiments (e.g., where the coating7 is one of the exemplary film stacks tabulated below) provide an IGunit 3 having a visible-thermal efficiency ratio of greater than 2.0 butless than 2.5, such as about 2.44.

Another useful parameter to consider is T₇₄₀, i.e., the transmittance at740 nm. The present coating 7 can provide a particularly low T₇₄₀, whileat the same time providing high levels of visible transmittance and goodcolor properties. For example, the present pane 12 preferably has a T₇₄₀of less than 0.30, or even less than 0.20. Perhaps more preferably, thepresent pane 12 (when monolithic, or when part of an insulating unit)has a T₇₄₀ of less than 0.15 (e.g., less than 0.1, or even less than0.05). While the desired level of transmittance at 740 nm can beselected and varied to accommodate different applications, certainpreferred embodiments (e.g., where the coating 7 is one of the exemplaryfilm stacks tabulated below) provide a coated pane 12 (which can bemonolithic or part of the IG unit 3) having a T₇₄₀ of about 0.04.

FIG. 4 exemplifies certain embodiments that provide a coated substrate12 having a major surface 18 bearing a high infrared reflection,low-emissivity coating 7. Generally, the coating includes, in sequencefrom the major surface 18 outwardly, a first transparent dielectric filmregion 20, a first infrared-reflection film region 100, a secondtransparent dielectric film region 40, a second infrared-reflection filmregion 200, a third transparent dielectric film region 60, a thirdinfrared-reflection film region 300, and a fourth transparent dielectricfilm region 80. In FIG. 4, optional blocker film regions 105, 205, 305are shown, although these are not required in all embodiments.

Each infrared-reflection film region 100, 200, 300 can advantageouslycomprise (optionally at least 50 atomic percent of, in some casesconsisting essentially on silver. Further, in some embodiments, thethickness of at least one of the infrared-reflection film regions 100,200, 300 is greater than 150 angstroms, greater than 175 angstroms, oreven greater than 200 angstroms. Additionally or alternatively, thefirst, second, and third infrared-reflection film regions can optionallyhave a combined thickness of greater than 425 Å, greater than 450 Å, oreven greater than 460 Å, such as about 477 Å. In some cases, the first,second, and third infrared-reflection film regions 100, 200, 300 aresilver layers having respective thicknesses of 122 Å, 149 Å, and 206 Å.

One group of embodiments provides a coated substrate (e.g., a coatedpane, such as a glass pane, optionally having a major dimension of atleast 1 meter, or at least 1.2 meters) bearing a low-emissivity coating7 that comprises three infrared reflection film regions 100, 200, 300having a combined thickness of between 420 Å and 575 Å.

The infrared-reflection film regions 100, 200, 300 are described belowin further detail. Briefly, though, some preferred embodiments providethese film regions in the form of silver layers each consistingessentially of silver, with these three layers optionally being the onlysilver layers in the coating. In one particular embodiment of thisnature, the substrate 12 is a glass sheet having a major dimension of atleast one meter (or at least 1.2 meters), and this glass sheet is partof a multiple-pane insulating glass unit that includes at least oneother glass sheet, where the multiple-pane unit has a between-pane space1500, which can optionally be evacuated, filled with air, or filled withair and insulative gas (e.g., argon).

The first transparent dielectric film region 20 is applied over (in somecases, directly over) a major surface 18 of the substrate 12. This filmregion 20 can be of any composition that includes at least some (or,optionally, consists essentially on transparent dielectric film. In somecases, the first transparent dielectric film region 20 is a singlelayer. In other cases, it comprises a plurality of layers. As describedin U.S. Pat. No. 5,296,302 (the teachings of which on useful dielectricmaterials are incorporated herein by reference), useful dielectric filmmaterials for this purpose include oxides of zinc, tin, indium, bismuth,titanium, hafnium, zirconium, and alloys thereof. Film comprisingsilicon nitride and/or silicon oxynitride can also be used.

The first transparent dielectric film region 20 can be a single layer ofa single dielectric material. If a single layer is used, it is generallypreferred that this inner dielectric layer be formed of a mixture ofzinc oxide and tin oxide (referred to below, e.g., in Table 1, as“Zn+O”). It should be understood, though, that such a single layer canbe replaced with two or more layers of different dielectric materials.In certain embodiments, the first transparent dielectric film region 20comprises a graded thickness of film, having a composition that changes(e.g., in a gradual manner) with increasing distance from the substrate12.

In some particular embodiments, the first transparent dielectric filmregion 20 comprises film (optionally comprising zinc oxide, such as azinc tin oxide) having a refractive index of 1.7 or greater. Forexample, between the first infrared-reflection film region 100 and thesurface 18 of the substrate 12, there can advantageously be provided adesired total thickness of film that has a refractive index of 1.7 orgreater. In some cases, this desired total thickness is less than 190angstroms, less than 175 angstroms, less than 165 angstroms, less than145 angstroms, or even less than 140 angstroms.

Referring again to FIG. 4, the first infrared-reflection film region isidentified by the reference number 100. This film region 100 preferablyis contiguous to, i.e., in direct physical contact with, the outer faceof the first transparent dielectric film region 20. Any suitableinfrared reflection material can be used. Silver, gold, and copper, aswell as alloys thereof, are the most commonly used infrared-reflectionfilm materials. Preferably, the infrared-reflection film consistsessentially of silver or silver combined with no more than about 5% ofanother metal, such as another metal selected from the group consistingof gold, platinum, and palladium. This, however, is by no meansrequired.

When desired for protection of the infrared-reflection film duringapplication of subsequent film and/or during any heat treatment (e.g.,tempering), a first blocker film region 105 can optionally be providedover and contiguous to the first infrared-reflection film region 100.This blocker film region 105 can be provided to protect the underlyinginfrared-reflection film region 100 from chemical attack. In such cases,any material that is, for example, readily oxidized may be useful. Incertain embodiments, a thin layer of titanium metal is applied, and insome cases (e.g., cases where oxide film is reactively depositeddirectly over such a blocker film region) at least an outermostthickness of that titanium metal is converted to titanium oxide ofvarying stoichiometry during deposition of overlying film. In anotherembodiment, the blocker film region 105 is deposited as a layer ofniobium. Useful blocker layers comprising niobium are discussed indetail in PCT International Publication No. WO 97/48649. The teachingsof this PCT Publication relating to blocker layers are incorporatedherein by reference. Other materials can be used, such as nickel,chromium, nickel-chrome, etc.

Exemplary thicknesses for the optional blocker film region generallyrange from 3-25 Å, such as 3-18 Å. Greater thicknesses can be used, ifdesired.

In one group of embodiments, the coating 7 comprises threeinfrared-reflection film regions directly over at least one of which(and optionally over each of which) there is provided a blocker filmregion that is deposited in a non-metallic form (e.g., as a non-metallicmaterial selected from the group consisting of an oxide, a nitride, andan oxynitride, including substoichiometric forms thereof). In this groupof embodiments, the thickness for each such blocker film region can bewithin any one of the ranges noted herein for the optional blocker filmregions. Related method embodiments involve sequentially depositing thefilm regions of any coating embodiment disclosed herein, in the processdepositing one or more blocker film regions in non-metallic form.

In certain preferred embodiments, the first blocker film region 105 hasa particularly small thickness, such as less than 15 Å, less than 10 Å,less than 7 Å, less than 6 Å, or even less than 5 Å. While not shown inFIG. 4, a blocker film region can optionally be provided under the firstinfrared-reflection film region 100 as well.

The second transparent dielectric film region 40 is positioned betweenthe first infrared-reflection film region 100 and the secondinfrared-reflection film region 200. Thus, the film region 40 can alsobe referred to as a “spacer” film region. This first spacer film region40 can be a single layer of a single transparent dielectric material, orit can be a plurality of layers of different transparent dielectricmaterials. In some cases, the second transparent dielectric film region40 comprises at least three transparent dielectric layers. Optionally,there are at least five, or even at least seven, such layers. As analternative to using one or more discrete layers, part or all of thesecond transparent dielectric film region 40 can have a gradedcomposition (optionally characterized by a gradual transition from onetransparent dielectric material to another with increasing distance fromthe substrate).

The next illustrated film region is the second infrared-reflection filmregion 200. This film region 200 preferably is contiguous to the outerface of the second transparent dielectric film region 40. Any suitableinfrared reflection material can be used, such as silver, gold, andcopper, or alloys including one or more of these metals. In someparticular embodiments, the infrared-reflection film consistsessentially of silver or silver combined with no more than about 5% ofanother metal, such as another metal selected from the group consistingof gold, platinum, and palladium.

When desired for protection of the second infrared-reflection filmregion 200, a second blocker film region 205 can optionally be providedover and contiguous to the second infrared-reflection film region 200.This blocker film region 205 can comprise any material that is, forexample, readily oxidized. In certain embodiments, a thin layer oftitanium metal is applied, and in some cases (e.g., cases where oxidefilm is reactively deposited directly over this blocker film region 205)at least an outermost thickness of that titanium metal is converted to atitanium oxide of varying stoichiometry during deposition of overlyingfilm. In another embodiment, the blocker film region 205 is deposited asa layer of niobium or one of the noted non-metallic blocker filmmaterials. Other materials can be used, such as nickel, chromium,nickel-chrome, etc.

Suitable thicknesses for the optional second blocker film region 205generally range from 3-25 Å, or 3-18 Å. Greater thicknesses can be used,if desired. In certain embodiments, the second blocker film region 205has a particularly small thickness, such as less than 15 Å, less than 10Å, less than 7 Å, less than 6 Å, or even less than 5 Å. While not shownin FIG. 4, a blocker film region can optionally be provided under thesecond infrared-reflection film region 200 as well.

The third transparent dielectric film region 60 is positioned betweenthe second infrared-reflection film region 200 and the thirdinfrared-reflection film region 300. This transparent dielectric filmregion 60 is also a spacer film region, and can be referred to as thesecond spacer film region. The third transparent dielectric film region60 can be a single layer of a single transparent dielectric material, orit can be a plurality of layers of different transparent dielectricmaterials. In some cases, the third transparent dielectric film region60 comprises at least three transparent dielectric layers. Optionally,there are at least five, or even at least seven, such layers. As analternative to one or more discrete layers, part or all of the thirdtransparent dielectric film region 60 can have a graded composition.

The next illustrated film region is the third infrared-reflection filmregion 300. This film region 300 preferably is contiguous to the outerface of the third transparent dielectric film region 60. Any suitableinfrared reflection material can be used (e.g., silver, gold, copper, oran alloy comprising one or more of these metals). In some particularembodiments, the third infrared-reflection film region 300 consistsessentially of silver or silver combined with no more than about 5% ofanother metal, such as another metal selected from the group consistingof gold, platinum, and palladium.

When desired for protection of the third infrared-reflection film region300, a third blocker film region 305 can optionally be provided over andcontiguous to the third infrared-reflection film region 300. Thisblocker film region 305 can comprise any material that is, for example,readily oxidized. In certain embodiments, a thin layer of titanium metalis applied, and in some cases (e.g., cases where oxide film isreactively deposited directly over this blocker film region 305) atleast an outermost thickness of that titanium metal is converted to atitanium oxide of varying stoichiometry during deposition of overlyingfilm. In another embodiment, the blocker film region 305 is deposited asa layer of niobium or one of the noted non-metallic blocker filmmaterials. Other materials can be used, such as nickel, chromium,nickel-chrome, etc.

Suitable thicknesses for the optional third blocker film region 305generally range from 3-25 Å, or 3-18 Å. Greater thicknesses can be used,if desired. In certain embodiments, the third blocker film region 305has a particularly small thickness, such as less than 15 Å, less than 10Å, less than 7 Å, less than 6 Å, or even less than 5 Å. While not shownin FIG. 4, a blocker film region can optionally be provided under thethird infrared-reflection film region 300 as well.

Given the large number of blocker film regions provided in certainembodiments, it can be advantageous to use an exceptionally smallthickness for one or more of the blocker film regions. Thus, in someembodiments, directly over at least one of the infrared-reflection filmregions there is provided a blocker film region having a thickness ofless than 7 Å, less than 6 Å, or even less than 5 Å. Further, in someembodiments, the coating 7 includes three blocker film regions 105, 205,305, and the combined thickness of all three of these blocker filmregions is less than 30 Å, less than 25 Å, less than 20 Å, less than 18Å, or even less than 15 Å.

The fourth transparent dielectric film region 80 is located further fromthe substrate 12 than the third infrared-reflection film region 300. Insome, though not all, embodiments, this film region 80 defines thecoating's outermost face 77 (which face can optionally be exposed, i.e.,not covered by any other film or substrate). The fourth transparentdielectric film region 80 can be a single layer of a single transparentdielectric material, or it can be a plurality of layers of differenttransparent dielectric materials. In some cases, the fourth transparentdielectric film region 80 comprises at least three transparentdielectric layers. Optionally, there are at least five, or even at leastseven, such layers. As an alternative to using one or more discretelayers, part or all of the fourth transparent dielectric film region 80can have a graded composition.

Thus, it can be appreciated that the present coating 7 desirablyincludes at least four transparent dielectric film regions 20, 40, 60,80. In some embodiments, the coating 7 comprises one or more, two ormore, or even three or more nitride or oxynitride films, such as atleast one, at least two, or even at least three films comprising siliconnitride and/or silicon oxynitride. In some embodiments of this nature,the coating 7 includes at least one nitride or oxynitride film(optionally comprising silicon nitride and/or silicon oxynitride) havinga thickness of less than 150 angstroms, less than 140 angstroms, or evenless than 125 angstroms, together with at least one other nitride oroxynitride film (optionally comprising silicon nitride and/or siliconoxynitride) having a thickness of greater than 50 angstroms, greaterthan 75 angstroms, greater than 100 angstroms, greater than 150angstroms, or even greater than 175 angstroms. In some cases, the latternoted film is located either between the first 100 and second 200infrared-reflection film regions or between the second 200 and third 300infrared-reflection film regions. That is, it forms (or is part on oneof the spacer film regions. Reference is made to Table 3 below.

The total thickness of the present coating 7 can be varied to suit therequirements of different applications. In certain preferredembodiments, the total physical thickness of the coating 7 is greaterthan 1,750 angstroms, greater than 1,800 angstroms, greater than 1,900angstroms, or even greater than 2,000 angstroms. For any embodimentdisclosed in this specification, the coating's total thickness canoptionally fall within any one or more of the ranges specified in thisparagraph.

In one particular group of embodiments, the thickness of the thirdinfrared-reflection film region 300 is greater than the thickness of thesecond infrared-reflection film region 200, and the thickness of thesecond infrared-reflection film region 200 is greater than the thicknessof the first infrared-reflection film region 100. This group ofembodiments is advantageous in terms of providing good reflected colorproperties. In one subgroup of these embodiments, the first 100, second200, and third 300 infrared-reflection film regions each comprise (orconsist essentially on silver.

For purposes of the present specification, the first reflection-regionratio is defined as being the thickness of the first infrared-reflectionfilm region 100 over the thickness of the second infrared-reflectionfilm region 200, and the second reflection-region ratio is defined asbeing the thickness of the second infrared-reflection film region 200over the thickness of the third infrared-reflection film region 300. Insome particular embodiments, at least one of the first and secondreflection-region ratios is less than 0.85, less than 0.83, or even lessthan 0.80. Optionally, the first and second reflection-region ratios areboth less than 0.83, such as about 0.819 and 0.723 respectively.

In some embodiments of the present group, the thickness of at least oneof the infrared-reflection film regions 100, 200, 300 is greater than150 Å, greater than 175 Å, or even greater than 200 Å. Additionally oralternatively, the first, second, and third infrared-reflection filmregions can optionally have a combined thickness of greater than 425 Å,greater than 450 Å, or even greater than 460 Å, such as about 477 Å. Insome cases, the first, second, and third infrared-reflection filmregions 100, 200, 300 are silver layers having respective thicknesses of122 Å, 149 Å, and 206 Å.

In some embodiments of the present group, the first transparentdielectric film region 20 comprises film (optionally comprising zincoxide, such as a zinc tin oxide) having a refractive index of 1.7 orgreater. For example, between the first infrared-reflection film region100 and the surface 18 of the substrate 12, there can advantageously beprovided a desired total thickness of film that has a refractive indexof 1.7 or greater. In certain embodiments, this desired total thicknessis less than 190 angstroms, less than 175 angstroms, less than 165angstroms, less than 145 angstroms, or even less than 140 angstroms.

For purposes of this disclosure, the primary dielectric-region ratio isdefined as being the thickness of the first transparent dielectric filmregion 20 over the thickness of the fourth transparent dielectric filmregion 80. This ratio can advantageously be less than 0.75, or even lessthan 0.6, while at the same time optionally being greater than 0.34,greater than 0.35, greater than 0.37, or even greater than 0.40. In oneexemplary embodiment, this ratio is about 0.47. A primarydielectric-region ratio within any one or more of these ranges canoptionally be adopted for any embodiment of the present group, or forany other embodiment disclosed in this specification.

Table 1 below shows one exemplary film stack that can be usedadvantageously as the high infrared reflection coating 7: TABLE 1 FILMSAMPLE A Zn + O 159 Å Ag 122 Å Ti  20 Å Zn + O 562 Å Ag 149 Å Ti  20 ÅZn + O 655 Å Ag 206 Å Ti  20 Å Zn + O 236 Å Si3N4 101 Å

Table 2 below illustrates three more exemplary film stacks that can beused advantageously as the high infrared reflection coating 7: TABLE 2FILM SAMPLE B SAMPLE C SAMPLE D Zn + O 165 Å 164 Å 164 Å Ag 117 Å 117 Å117 Å Ti  20 Å  20 Å  30 Å Zn + O 591 Å 592 Å 591 Å Ag 154 Å 147 Å 154 ÅTi  20 Å  20 Å  35 Å Zn + O 665 Å 665 Å 665 Å Ag 206 Å 208 Å 206 Å Ti 20 Å  20 Å  35 Å Zn + O 214 Å 214 Å 210 Å Si3N4 100 Å 100 Å 100 Å

Table 3 below illustrates yet another exemplary film stack that can beused advantageously as the high infrared reflection coating 7: TABLE 3FILM SAMPLE E Zn + O 159 Å Ag 122 Å Ti  20 Å Zn + O 562 Å Ag 149 Å Ti 20 Å Zn + O 235 Å Si3N4 185 Å Zn + O 235 Å Ag 206 Å Ti  20 Å Zn + O 236Å Si3N4 101 Å

The present invention includes methods of producing a coated substrate,e.g., a coated glass pane. The invention provides method embodimentswherein the film regions of any coating embodiment disclosed herein aresequentially deposited using any one or more thin film depositiontechniques. In accordance with the present methods, a substrate 12having a surface 18 is provided. If desired, this surface 18 can beprepared by suitable washing or chemical preparation. The presentcoating 7 is deposited on the surface 18 of the substrate 12, e.g., as aseries of discrete layers, as a thickness of graded film, or as acombination including at least one discrete layer and at least onethickness of graded film. The coating can be deposited using anysuitable thin film deposition technique. One preferred method utilizesDC magnetron sputtering, which is commonly used in industry. Referenceis made to Chapin's U.S. Pat. No. 4,166,018, the teachings of which areincorporated herein by reference.

Briefly, magnetron sputtering involves transporting a substrate througha series of low pressure zones (or “chambers” or “bays”) in which thevarious film regions that make up the coating are sequentially applied.Metallic film is sputtered from metallic sources or “targets,” typicallyin an inert atmosphere such as argon. To deposit transparent dielectricfilm, the target may be formed of the dielectric itself (e.g., zincoxide or titanium oxide). More commonly, though, the dielectric film isapplied by sputtering a metal target in a reactive atmosphere. Todeposit zinc oxide, for example, a zinc target can be sputtered in anoxidizing atmosphere; silicon nitride can be deposited by sputtering asilicon target (which may be doped with aluminum or the like to improveconductivity) in a reactive atmosphere containing nitrogen gas. Thethickness of the deposited film can be controlled by varying the speedof the substrate and/or by varying the power on the targets.

Another method for depositing thin film on a substrate involves plasmachemical vapor deposition. Reference is made to U.S. Pat. No. 4,619,729(Johncock et al.) and U.S. Pat. No. 4,737,379 (Hudgens et al.), theteachings of both of which are incorporated herein by reference. Suchplasma chemical vapor deposition involves the decomposition of gaseoussources via a plasma and subsequent film formation onto solid surfaces,such as glass substrates. The film thickness can be adjusted by varyingthe speed of the substrate as it passes through a plasma zone and/or byvarying the power and/or gas flow rate within each zone.

Turning now to FIG. 6, there is depicted an exemplary method fordepositing a high infrared reflection coating 7 in accordance withcertain embodiments of the invention. The coater shown schematically inFIG. 6 is used to deposit a coating 7 that includes, in sequence fromthe major surface 18 outwardly, a first transparent dielectric filmregion 20 comprising zinc tin oxide, a first infrared-reflection filmregion 100 comprising silver, a first blocker film region 105 comprisingtitanium, a second transparent dielectric film region 40 comprising zinctin oxide, a second infrared-reflection film region 200 comprisingsilver, a second blocker film region 205 comprising titanium, a thirdtransparent dielectric film region 60 comprising zinc tin oxide, a thirdinfrared-reflection film region 300 comprising silver, a third blockerfilm region 305 comprising titanium, and a fourth transparent dielectricfilm region 80 that includes an outermost layer comprising siliconnitride over a layer comprising zinc tin oxide.

With continued reference to FIG. 6, the substrate 12 is positioned atthe beginning of the coater and conveyed into the first coat zone CZ1(e.g., by conveying the substrate along transport rollers 10). This coatzone CZ1 is provided with three sputtering chambers (or “bays”), C1through C3, which are adapted collectively to deposit a firsttransparent dielectric film region 20 comprising zinc tin oxide. Allthree of these bays are provided with sputtering targets comprising acompound of zinc and tin. Each of these bays is illustrated as havingtwo cylindrical sputtering targets, although the number and type (e.g.,cylindrical versus planar) can be varied as desired. These first sixtargets are sputtered in an oxidizing atmosphere to deposit the firsttransparent dielectric film region 20 in the form of an oxide filmcomprising zinc and tin. The oxidizing atmosphere here can consistessentially of oxygen (e.g., about 100% O₂) at a pressure of about4×10⁻³ mbar. Alternatively, this atmosphere may comprise argon andoxygen. With reference to Table 4 below, a power of about 36.7 kW isapplied to the first two targets, a power of about 34.6 kW is applied tothe second two targets, and a power of about 35.5 kW is applied to thethird two targets. The substrate 12 is conveyed beneath all six of thesetargets at a rate of about 310 inches per minute, while sputtering eachtarget at the noted power level, thereby depositing the firsttransparent dielectric film region 20 in the form of an oxide filmcomprising zinc and tin and having a thickness of about 159 angstroms.

The substrate 12 is then conveyed into a second coat zone CZ2 whereinthe first infrared-reflection film region 100 is applied directly overthe first transparent dielectric film region 20. The second coat zoneCZ2 is provided with an inert atmosphere (e.g., argon at a pressure ofabout 4×10⁻³ mbar). The active sputtering bays C4 and C5 of this coatzone CZ2 each have a planar target, although the number and type oftargets can be changed. The target in bay C4 is a metallic silvertarget, whereas the target in bay C5 is a metallic titanium target. Thesubstrate is conveyed beneath the silver target at a rate of about 310inches per minute, while sputtering this target at a power of about 7.1kW, thereby depositing the first infrared-reflection film region 20 inthe form of a silver film having a thickness of about 122 angstroms. Thesubstrate is then conveyed beneath the titanium target in bay C5, whilesputtering this target at a power of about 7.8 kW, thereby depositing afirst blocker film region 105 in the form of a film comprising titaniumand having a thickness of about 20 angstroms.

The substrate 12 is then conveyed through a third coat zone CZ3, afourth coat zone CZ4, and a fifth coat zone CZ5, in which zones thesecond transparent dielectric film region 40 is applied in the form ofan oxide film comprising zinc and tin. The third CZ3 and fourth CZ4 coatzones each have three active sputtering bays. The fifth coat zone CZ5has two active sputtering bays (there may be unused bays and/or coatzones along the way). In each of the bays C6-C13, there are mounted twocylindrical targets each comprising (i.e., including a sputterabletarget material comprising) a compound of zinc and tin. Each of thesesputtering bays C6-C13 is provided with an oxidizing atmosphere. Forexample, the oxidizing atmospheres in the third CZ3, fourth CZ4, andfifth CZ5 coat zones can each consist essentially of oxygen (e.g., about100% O₂) at a pressure of about 4×10⁻³ mbar. Alternatively, one or moreof these atmospheres can comprise argon and oxygen.

As shown in Table 4 below, a power of about 50.2 kW is applied to thefirst two targets in the third coat zone CZ3, a power of about 45.1 kWis applied to the second two targets in this coat zone CZ3, and a powerof about 49.5 kW is applied to the third two targets in this zone CZ3.Here, a power of about 53.1 kW is applied to the first two targets inthe fourth coat zone CZ4, a power of about 47.7 kW is applied to thesecond two targets in this coat zone CZ4, and a power of about 44.8 isapplied to the third two targets in this zone CZ4. Further, a power ofabout 49.0 kW is applied to the first two targets in the fifth coat zoneCZ5, and a power of about 45.6 kW is applied to the second two targetsin this coat zone CZ5. The substrate 12 is conveyed beneath all of thenoted targets in coat zones 3-5 (i.e., CZ3 through CZ5), while conveyingthe substrate at a rate of about 310 inches per minute and sputteringeach target at the noted power level, such that the second transparentdielectric film region 40 is applied in the form of an oxide filmcomprising zinc and tin and having a thickness of about 562 angstroms.

The substrate 12 is then conveyed into a sixth coat zone CZ6 wherein thesecond infrared-reflection film region 200 is applied directly over thesecond transparent dielectric film region 40. The sixth coat zone CZ6has an inert atmosphere (e.g., argon at a pressure of about 4×10⁻³mbar). The sputtering bays C14, C15 in this coat zone CZ6 each have aplanar target. The target in bay C14 is a metallic silver target, andthe target in chamber C15 is a metallic titanium target. A power ofabout 8.9 kW is applied to the silver target, while the substrate isconveyed beneath this target at a rate of about 310 inches per minute,to deposit the second infrared-reflection film region 200 as a metallicsilver film having a thickness of about 149 angstroms. The substrate isthen conveyed (at the same speed) beneath the metallic titanium targetin bay C15, with a power of about 8.1 kW being applied to this target,to deposit a second blocker film region 205 comprising titanium andhaving a thickness of about 20 angstroms.

The substrate 12 is then conveyed through a seventh coat zone CZ7, aneighth coat zone CZ8, and a ninth coat zone CZ9, wherein collectivelythe third transparent dielectric film region 60 is applied. Each ofthese coat zones has three sputtering bays, and each such bay isprovided with two cylindrical targets (bays C16 through C18 are in CZ7,bays C19 through C21 are in CZ8, and bays C22 through C24 are in CZ9).The targets here all comprise a sputterable material that is a compoundof zinc and tin. Each of these coat zones is provided with an oxidizingatmosphere consisting essentially of oxygen (e.g., about 100% O₂ at apressure of about 4×10⁻³ mbar). Alternatively, this atmosphere maycomprise argon and oxygen.

A power of about 50.3 kW is applied to the first two targets in theseventh coat zone CZ7, a power of about 45.5 kW is applied to the secondtwo targets in this coat zone CZ7, and a power of about 48.9 kW isapplied to the third two targets in this zone CZ7. A power of about 52.5kW is applied to the first two targets in the eighth coat zone CZ8,while a power of about 48.2 kW is applied to the second two targets inthis coat zone CZ8, and a power of about 44.7 kW is applied to the thirdtwo targets in this zone CZ8. A power of about 49.0 kW is applied to thefirst two targets in the ninth coat zone CZ9, while a power of about45.5 kW is applied to the second two targets in this coat zone CZ9, anda power of about 47.8 kW is applied to the third two targets in thiszone CZ9. The substrate 12 is conveyed beneath all of these targets(i.e., beneath all of the targets in CZ7 through CZ9) at a rate of about310 inches per minute, while sputtering each target at the noted powerlevel, such that the third transparent dielectric film region 60 isapplied as an oxide film comprising zinc and tin and having a thicknessof about 655 angstroms.

The substrate 12 is then conveyed into a tenth coat zone CZ10 where thethird infrared-reflection film region 300 is applied. This coat zoneCZ10 contains an inert atmosphere (e.g., argon at a pressure of about4×10⁻³ mbar). The active bays C25, C26 in this coat zone CZ10 are eachprovided with a planar target. The target in bay C25 is a metallicsilver target, and the target in bay C26 is a metallic titanium target.A power of about 12.6 kW is applied to the silver target, while thesubstrate is conveyed beneath this target at a rate of about 310 inchesper minute, thereby depositing the third infrared-reflection film region300 as a silver film having a thickness of about 206 angstroms. Thesubstrate is then conveyed beneath the titanium target in chamber C26,while sputtering that target at a power level of about 8.1 kW, so as todeposit a third blocker film region 305 in the form of a film comprisingtitanium and having a thickness of about 20 angstroms.

The substrate 12 is then conveyed through an eleventh coat zone CZ11, atwelfth coat zone CZ12, and a thirteenth coat zone CZ13, whereincollectively there is deposited an inner portion of the fourthtransparent dielectric film region 80. The eleventh coat zone C11 hasthree sputtering bays, each with two cylindrical targets (bays C27through C29 are in CZ11). The twelfth coat zone C12 has only one activesputtering bay C30, and this bay C30 is provided with two cylindricaltargets. The thirteenth coat zone CZ13 has three sputtering bays, eachprovided two cylindrical targets (bays C31 through C33 are in CZ13).Each of the noted targets in coat zones CZ11 through CZ13 comprises asputterable target material that is a compound of zinc and tin. The coatzones CZ11 through CZ13 are all provided with oxidizing atmospheres,each consisting essentially of oxygen (e.g., about 100% O₂ at a pressureof about 4×10⁻³ mbar). Alternatively, one or more of these atmospherescan comprise argon and oxygen.

A power of about 17.9 kW is applied to the first two targets in theeleventh coat zone CZ11, a power of about 21.1 kW is applied to thesecond two targets in this coat zone CZ11, and a power of about 19.6 kWis applied to the third two targets in this zone CZ11. A power of about20.1 kW is applied to the two targets in the twelfth coat zone CZ12. Apower of about 21.5 kW is applied to the first two targets in thethirteenth coat zone CZ13, a power of about 19.4 kW is applied to thesecond two targets in this coat zone CZ13, and a power of about 19.3 kWis applied to the third two targets in this zone CZ13. The substrate 12is conveyed beneath all of the noted targets in CZ11 through CZ13 at arate of about 310 inches per minute, while sputtering each of thesetargets at the noted power level, such that an inner portion of thefourth transparent dielectric film region 80 is applied as an oxide filmcomprising zinc and tin and having at a thickness of about 236angstroms.

Finally, the substrate is conveyed into a fourteenth coat zone CZ14,wherein the outermost portion of the fourth transparent dielectric filmregion 80 is applied. This zone CZ14 has three sputtering bays C34-C36,each containing a nitrogen atmosphere, optionally with some argon, at apressure of about 4×10⁻³ mbar. The bays C34 through C36 in this coatzone CZ14 are each provided with two cylindrical targets. Each of thesetargets comprises a sputterable target material of silicon with a smallamount of aluminum. A power of about 31.9 kW is applied to the first twotargets in the fourteenth zone CZ14, a power of about 34.0 kW is appliedto the second two targets in this zone CZ14, and a power of about 37.4kW is applied to the third two targets in this zone CZ14. The substrate12 is conveyed beneath all of the targets in CZ14 at a rate of about 310inches per minute, while sputtering each of these targets at the notedpower level, such that the outermost portion of the fourth transparentdielectric film region 80 is applied as a nitride film comprisingsilicon and a small amount of aluminum and having a thickness of about101 angstroms. TABLE 4 Bay Power (kW) C1 36.7 C2 34.6 C3 35.5 C4 7.1 C57.8 C6 50.2 C7 45.1 C8 49.5 C9 53.1 C10 47.7 C11 44.8 C12 49 C13 45.6C14 8.9 C15 8.1 C16 50.3 C17 45.5 C18 48.9 C19 52.5 C20 48.2 C21 44.7C22 49 C23 45.5 C24 47.8 C25 12.6 C26 8.1 C27 17.9 C28 21.1 C29 19.6 C3020.1 C31 21.5 C32 19.4 C33 19.3 C34 31.9 C35 34 C36 37.4

While some preferred embodiments of the invention have been described,it should be understood that various changes, adaptations andmodifications may be made therein without departing from the spirit ofthe invention and the scope of the appended claims.

1. A substrate having a major surface that bears a low-emissivitycoating, the coating comprising a first infrared-reflection film regionhaving a thickness, a second infrared-reflection film region having athickness, and a third infrared-reflection film region having athickness, where the thickness of the third infrared-reflection filmregion is greater than the thickness of the second infrared-reflectionfilm region, and the thickness of the second infrared-reflection filmregion is greater than the thickness of the first infrared-reflectionfilm region, the coating comprising, from said major surface outwardly:a) a first transparent dielectric film region; b) the firstinfrared-reflection film region; c) a second transparent dielectric filmregion; d) the second infrared-reflection film region; e) a thirdtransparent dielectric film region; f) the third infrared-reflectionfilm region; g) a fourth transparent dielectric film region; wherein thefirst, second, and third infrared-reflection film regions each comprisesilver, wherein the coating has a first reflection-region ratio equal tothe thickness of the first infrared-reflection film region over thethickness of the second infrared-reflection film region, the coating hasa second reflection-region ratio equal to the thickness of the secondinfrared-reflection film region over the thickness of the thirdinfrared-reflection film region, and wherein at least one of said firstand second reflection-region ratios is less than 0.85.
 2. The substrateof claim 1 wherein at least one of said first and secondreflection-region ratios is less than 0.80.
 3. The substrate of claim 1wherein said first and second reflection-region ratios are both lessthan 0.83.
 4. The substrate of claim 1 wherein the first transparentdielectric film region comprises film having a refractive index of 1.7or greater, and wherein between the first infrared-reflection filmregion and said major surface of the substrate there is a desired totalthickness of film that has a refractive index of 1.7 or greater, saiddesired total thickness being less than 190 angstroms.
 5. The substrateof claim 4 wherein said desired total thickness is less than 175angstroms.
 6. The substrate of claim 4 wherein the low-emissivitycoating has a total thickness of greater than 1,800 angstroms.
 7. Thesubstrate of claim 4 wherein the low-emissivity coating has a totalthickness of greater than 1,900 angstroms.
 8. The substrate of claim 1wherein the thickness of at least one of the infrared-reflection filmregions is greater than 150 angstroms.
 9. The substrate of claim 1wherein the thickness of at least one of the infrared-reflection filmregions is greater than 200 angstroms.
 10. The substrate of claim 1wherein the coating has a primary dielectric-region ratio defined asbeing the thickness of the first transparent dielectric film region overthe thickness of the fourth transparent dielectric film region, saidprimary dielectric-region ratio being less than 0.75.
 11. The substrateof claim 10 wherein said primary dielectric-region ratio is less than0.6.
 12. The substrate of claim 1 wherein the first, second, and thirdinfrared-reflection film regions have a combined thickness of greaterthan 425 angstroms.
 13. The substrate of claim 12 wherein the combinedthickness of the first, second, and third infrared-reflection filmregions is greater than 450 angstroms.
 14. The substrate of claim 1wherein the coated substrate has a total visible transmission of greaterthan 55%.
 15. The substrate of claim 14 wherein the total visibletransmission is greater than 60%.
 16. The substrate of claim 14 whereinthe total visible transmission is greater than 65%.
 17. The substrate ofclaim 1 wherein the coated substrate has an emissivity of less than0.02.
 18. The substrate of claim 17 wherein the emissivity is less than0.015.
 19. The substrate of claim 1 wherein the first, second, and thirdinfrared-reflection film regions are silver layers each consistingessentially of silver, and wherein these three silver layers are theonly silver layers in the coating.
 20. The substrate of claim 19 whereinthe substrate is a glass sheet having a major dimension of at least onemeter, and wherein said glass sheet is part of a multiple-paneinsulating glass window unit that includes at least one other glasssheet, wherein the multiple-pane insulating glass window unit has abetween-pane space.